Optical Properties of Multi-Component Antimony-Silver Nanoclusters Formed in Silica by Sequential Ion Implantation
- PDF / 1,410,374 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 89 Downloads / 221 Views
the composite that are not possible with colloids composed of single elements.[ 1-41 The linear and nonlinear optical properties of these metal colloid-glass composites can be described using effective medium theory for small non interacting particles in a dielectric.[51 An increase in the nonlinear response of the composite near the surface plasmon resonance (SPR) frequency is expected with increasing volume fraction of metal. This enhancement is due to local field effects and is a consequence of dielectric confinement. The linear response for colloids with diameters less than ,/20, where X is the wavelength of the incident radiation, is reasonably described by effective medium theory in the electric dipole approximation[61 and is given by _187[n,
P•
---d .
Pc2
1, + 2nd212 +2
S
(1)
where (x is the absorption coefficient, e(k) = P-1+ i E2 is the dielectric constant of the metal, p is the volume fraction of the metal particles, and nd is the index of refraction of the dielectric host. The absorption is expected to exhibit a peak at the surface plasmon resonance frequency for which the condition ct+2n2 = 0 is met. The surface plasmon resonance frequency depends on the electronic properties of the metal colloids and on the index of refraction of the host dielectric, .(3)
nd. The third order nonlinear susceptibility, Xcff ' can be expressed as 391 Mat. Res. Soc. Symp. Proc. Vol. 396 © 1996 Materials Research Society
(
2 = pfC (0)lf 2(w)12 XIm3 with
(
=
3 n) Et + 2n(
and where fc(co) is the local field factor and x() is the nonlinear susceptibility of the metal colloids. The index of refraction and the intensity dependent term are related to the above quantities by[7] n = no+n 21 and n 2 = 1-21-Re[X43, (3) no where n. is the linear index of refraction and n2 is the intensity dependent component. From equation (2), a potentially large enhancement of the effective nonlinear susceptibility and in turn n2 is possible near or at the surface plasmon resonance frequency due to local field effects. Here we report on the optical response of nanometer dimension metal colloids formed by sequential implantation of Ag and Sb. Ag and Sb were chosen because of their fundamentally different dielectric properties and their observed nonlinear response in metal nanocluster glass composites.[8, 9, 10] EXPERIMENT First Ag and then Sb ions were sequentially implanted in Coming 7940 high purity silica substrates at energies that overlaid the depths of implantation for each metal. The Ag ions were implanted at 305 keV while the Sb ions were implanted at 320 keV, with substrate temperatures 16 2 of - 270" K and current densities of - 2 glamps/cm for both ions. Doses were 3 and 6x10 2 16 2 ions/cm for the Ag and 6 and 9x10 ions/cm for the Sb implantations. The sequentially implanted samples have a total nominal dose of 12x1016 ions/cm 2 with relative ratios of Ag to Sb of 3/9 and 6/6. Single element implanted samples were also fabricated for comparison. These samples were implanted to nominal doses of 3 and 6x10 16 ions/cm 2 for A
Data Loading...
